This invention relates to printed re-routing for wafer level packaging.
The process of manufacturing semiconductors, or Integrated Circuits (commonly called ICs, or chips) typically consists of numerous distinct processes during which hundreds of copies of an IC are formed on a single wafer.
The manufacturing process involves forming various patterned layers on and into the substrate, ultimately forming the completed IC. This layering process creates electrically active regions in and on the semiconductor wafer surface.
Following a process known as xe2x80x9cdie singulation,xe2x80x9d the individual dies that make up the wafer are assembled into wafer level packages that provide various interconnections for electrical contact between printed circuit boards (PCBs) and the singulated dies or ICs. Various types of high-density packaging technologies exist, such as Flip Chip and Chip Size Packages (CSP).
High-density packaging technologies such as CSP provide many advantages, e.g., reduced sizes, reduced weights, and more reliable electrical connections achievable with wafer level and bare die packaging configurations. However, broad applications of CSP packaging technology have been limited. A major difficulty is the production cost due to the processing complexity of wafer level packaging processes.
According to one aspect of the invention, a method for forming printed re-routing for wafer level packaging features forming a contact layer and a conductive redistribution structure on a semiconductor die.
The printed re-routing method further includes etching the contact layer of the die by using the conductive redistribution structure as a self-aligning mask.
One or more of the following features may also be included. Forming the contact layer includes realizing semiconductor defining processes on the contact layer of the semiconductor die. The semiconductor structure defining processes include providing contact pads made of a conductive material such as metals and metal alloys. Further, a passivation layer formed of a dielectric material such as a polyimide, is deposited on the die contact layer, serving as a barrier layer.
The structure defining processes further include forming a metal layer on the contact layer of the die by sputtering a conductive material onto the passivation layer. The metal layer provides the required stable electrical contact between the contact pads and the conductive redistribution structure.
As another feature, stencil printing is used for realizing the semiconductor structure defining processes.
As yet another feature, conductive polymers such as Isotropic Conductive Adhesive (ICA) and the glues are used to generate the redistribution lines, which include two ends, the first end including a ring recess and a guide region serving as a bump stop for retaining the interconnect bump and preventing the outflow of the bump material. The interconnect bump material can be solder paste or conductive polymer and may also include an under bump material that is nonconductive. The conductive redistribution structure is also used as a self-aligning mask for etching the metal layer.
According to another aspect of the invention, a semiconductor die includes a contact layer, contact pads attached to the contact layer of the die in a non-peripheral region, a passivation layer, and a metal layer deposited onto the passivation layer.
The semiconductor die further includes a pad re-routing trace on the contact layer of the die. In this aspect, the pad re-routing trace comprises a conductive redistribution structure formed on the metal layer by a printing process and a conductive interconnect bump. The conductive interconnect bump is connected to the conductive redistribution structure as an interconnection between the contact layer of the semiconductor die and a carrier surface. The semiconductor die further includes a metal layer etch on the contact layer caused by using the conductive redistribution structure as a self-aligning mask for etching.
One or more of the following features may also be included.
The contact pads are made from a conductive material selected from a group comprising metals and metal alloys. The passivation layer on the contact layer serves as a barrier layer and is formed of a dielectric material selected from a group comprising a polyimide. The conductive material of the redistribution lines is formed from a group comprising conductive polymers such as ICA and glues.
Another feature of the semiconductor die include the redistribution line. The redistribution line includes a first and a second end, the first end including a bump region having a ring recess and a guide region that serves as a bump stop for surrounding and retaining the interconnect bump to prevent the outflow of the bump material. The interconnect bump material can be solder paste or a conductive polymer.
As another feature, the semiconductor die may further include a nonconductive under bump material deposited onto the contact layer of the die prior to forming a conductive redistribution structure on the contact layer of the die.
Embodiments may have one or more of the following advantages.
The method for forming pad re-routing traces on a semiconductor die significantly decreases the complexity and costs for generating redistribution structures in wafer level packaging. The expensive processes using semiconductor processing equipment for photolithography and plating can be discarded, leading to quite practical and desirable advantages. The expensive processes required in photolithography such as spin resist, curing, exposing, and developing the redistribution structures are replaced by the concise processes of the present invention. The photoresist coating and patterning of an etch mask are no longer required, neither are the use of stripping set tools nor separate mask production. Thus, the number of processes are reduced, leading to greater production efficiency.
Furthermore, using the redistribution structure as a self-aligning mask improves alignment since only one material is used. This optimizes performance relative to field metal etch conditions.
Another benefit is that better compliance in the composite structure is obtained by using ICA to form the interconnect bump as well as the redistribution structures.
Further benefits include the uncoupling between the die contact pad material and the ICA of the redistribution structure, especially in the case of aluminum pads, where there is significant electrical interaction between the redistribution structure and the contact pad leading to unstable conditions. In particular, the use of printed ICA redistribution structure provides a concise and cost-effective method for etching the metal layer, providing a self-adjusting process where no complex photolithography processes are required.
Using the present method, a semiconductor die can be manufactured with fewer process steps. Accordingly, the materials and the yields of each production process of the present invention are improved and the use of manufacture equipment and the complexity involved in implementing the present method and semiconductor die are significantly decreased. Therefore, the goal of achieving a low cost CSP package manufactured by simple processing to produce highly reliable IC packages can be efficiently and productively achieved. Meeting the industry""s need for high-density packaging without an unacceptable packaging cost burden at the system level is possible.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.